Gusseted bag

ABSTRACT

To provide a gusseted tubular article made of heat-sealable resin for making a bag which is not liable to be broken in the heat-sealed section even when a heavy load is put in it and a gusseted composite tubular article on the outside of which a different material is put.  
     More specifically the preferred heat-sealable resin is a polyethylene-type resin comprising 100 to more than 50 wt % of linear low density polyethylene having density of 0.895 to 0.925 g/cm 3  and MFR of 0.1 to 10 g/10 minute, and 0 to less than 50 wT % of high-pressure low density polyethylene having density of 0.910 to 0.930 g/cm 3  and MFR of 0.1 to 10 g/10 minute.

TECHNICAL FIELD

[0001] The present invention relates to a gusseted tubular article made of polyethylene-type resin for making a bag, a gusseted tubular article for making a bag which includes the aforesaid gusseted tubular article in its structure, and a gusseted bag which can be obtained from these articles.

TECHNICAL BACKGROUND

[0002] Because of the technological advances in pharmaceuticals and electronic parts, it has now become necessary to take special care in the transportation of their raw materials and products and against the entry of foreign materials. Furthermore, similarly in the field of food and precooked food products, it has also become necessary to take special care to prevent foreign materials from getting into such products to maintain quality and keep them in satisfactory hygienic condition.

[0003] To meet such needs, resin bags made of synthetic resins such as polyolefin and polyester have been proposed. While these resin bags have excellent properties with respect to preventing the entry of foreign materials and keeping products in satisfactory hygienic condition, they have been found liable to be punctured or broken due to scratches or impact in transit.

[0004] For this reason, resin bags of such structure that they are covered with kraft paper, among other things, as the outer layer have been proposed to protect the bags. When those bags comprising a simple tubular article are stacked with goods packed in them, a collapse of such stack of the bags may occur because their surfaces are not flat. Because of this, a bag comprising a gusseted tubular article has been proposed (Japanese Patent Publication HEI 6-37218). In the Japanese Patent Publication, a structure is proposed in which the inner layer tubular article is made of a heat-sealable material and the outer layer is made of kraft paper.

[0005] With the conventionally known bag-making materials, however, gusseted bags made of such materials has a section in which the four tubular article layers are heat-sealed so that the end section of the gusseted tubular article is heat-sealed. Due to this, the gusseted bags made of such materials are liable to be broken in such heat-sealed section when a heavy load is packed in them.

[0006] Moreover, a bag which is so structured that its tubular article made of a heat-sealable material is covered with kraft paper, etc., as the outer layer is suitable for use in an environment in which the entry of foreign materials as mentioned above should be avoided. The reason is that after such bag covered with kraft paper has been transported, the tubular article made of a heat-sealable material can be taken out of the bag and brought to the site of work, after dust is removed from the bag and as required, treatment such as disinfection is given to the bag. However, there has been a possibility that the bags made of such conventionally known materials may be broken at the heat-sealed section as mentioned above.

[0007] The inventors of the present invention came up with it after they concentrated their efforts to develop those gusseted bags that are not liable to be broken in transit even when a heavy load is packed in them.

DISCLOSURE OF THE INVENTION

[0008] The present invention provides a gusseted tubular resin article made of heat-sealable resin which is less liable to be broken in the heat-sealed section even when a heavy load is packed in it.

[0009] The present invention provides a tubular resin article suitable for use as the inner-layer gusseted tubular article of the bag-making material comprising a gusseted tubular resin article having the characteristics described above and a gusseted tubular article made of a different material which is put on the outside of the former gusseted tubular resin article.

[0010] Furthermore, the present invention provides a material that can be used to form a gusseted composite tubular article which comprises a gusseted tubular article made of a heat-sealable resin having the characteristics described above and a gusseted tubular article made of a different material that is put on the outside of the former gusseted tubular resin article, and which can be sealed in the closing sections at its bottom and at its top.

[0011] The present invention provides a gusseted tubular article for making a bag which is made of a polyethylene-type resin comprising 100 to more than 50 weight percent of linear low density polyethylene having density of 0.895 to 0.925 g/cm³ and a melt flow rate of 0.1 to 10 g/10 minute and 0 to less than 50 weight percent of high-pressure low density polyethylene having density of 0.910 to 0.930 g/cm³ and a melt flow rate of 0.1 to 10 g/10 minute.

[0012] The present invention provides a gusseted bag obtained by heat-sealing the gusseted tubular article for making a bag mentioned above.

[0013] The present invention also provides a gusseted composite tubular article for making a bag which comprises the gusseted tubular article made of the polyethylene-type resin as specified above and a gusseted tubular article made of a different material which is put on the outside of the former gusseted tubular article.

[0014] The aforesaid gusseted composite tubular article for making a bag in which the aforesaid different material is kraft paper is a preferable embodiment of the present invention.

[0015] The aforesaid gusseted composite tubular article for making a bag in which the gusseted tubular article is so structured that both of its ends can be sealed is a preferable embodiment of the present invention.

[0016] The present invention provides a composite gusseted bag wherein a bottom section of the gusseted composite tubular article for making a bag is so structured that one of its ends is in alignment in a straight line at the end edge, and the end is heat-sealed and folded, and then the end is enclosed and fixed by means of a reinforcing paper with an opening tape to form the bottom end.

[0017] A composite gusseted bag in which the opening end of the tubular article has either a stairstepped section formed by extruding layers like stairs or at least one auxiliary flap so bonded to the outside wall surface that it forms a stairstepped surface protruding outside which can seal the opening end with a hot melt adhesive coated on its surface is a preferable embodiment of the present invention.

A BRIEF EXPLANATION OF THE DRAWINGS

[0018]FIG. 1 is a front view of an example of the gusseted tubular article of the present invention which comprises polyethylene-type resin

[0019]FIG. 2 is a front view of an example of the gusseted tubular article of the present invention.

[0020]FIG. 3 is a schematic view of the longitudinal cross-sectional view of the gusseted composite tubular article shown in FIG. 2.

[0021]FIG. 4 is a schematic view showing an example of the gusseted composite tubular article shown in FIG. 2 which is sealed at its bottom end.

[0022]FIG. 5 is a schematic view showing an example in which the end of the gusseted composite tubular article shown in FIG. 4 which has been folded once is sealed.

[0023]FIG. 6 is a schematic view showing an example in which the end of the inner layer gusseted tubular article shown in FIG. 5 which is made of polyethylene-type resin is sealed with the heat-sealing location having been changed

[0024]FIG. 7 is a schematic view showing an example in which the end shown in FIG. 4 is sealed with either inner or outer layer not being folded is sealed.

[0025]FIG. 8 is a schematic view showing an example in which the top end of the gusseted composite tubular article shown in FIG. 2 is sealed.

SPECIFIC EMBODIMENTS OF THE INVENTION

[0026] The present invention provides a gusseted tubular article for use as a bag which is made of a polyethylene-type resin comprising 100 to more than 50 weight percent of linear low density polyethylene having density of 0.895 to 0.925 g/cm³ and a melt flow rate of 0.1 to 10 g/10 minute and 0 to less than 50 weight percent of high-pressure low density polyethylene having density of 0.910 to 0.930 g/cm³ and a melt flow rate of 0.1 to 10 g/10 minute.

[0027] The present invention also provides a gusseted composite tubular article which comprises the gusseted tubular article made of heat-sealable resin and a gusseted tubular article made of a different material which is put on the outside of the former gusseted tubular article, wherein the heat-sealable material being the aforesaid polyethylene-type resin.

[0028] The polyethylene-type resin of the present invention is linear low density polyethylene having density of 0.895 to 0.925 g/cm³ and a melt flow rate of 0.1 to 10 g/10 minute or a composition of this linear low density polyethylene and the high-pressure low density polyethylene having density of 0.910 to 0.930 g/cm³ and a melt flow rate of 0 1 to 10 g/10 minute which is less in weight than the linear low density polyethylene.

[0029] The density of the linear′ low density polyethylene (LLDPE) of the present invention is preferably not more than 0.925, more preferably 0.895 to 0.925 g/cm³, much more preferably 0.900 to 0.925 g/cm³, and especially preferably 0.905 to 0.915 g/cm³.

[0030] The linear low density polyethylene used in the present invention is a common homopolymer of ethylene or a copolymer of ethylene and another α-olefin. Examples of such α-olefin includes α-olefins having 3 to 12, preferably 3 to 8, carton atoms, such as propylene, butene-1, pentene-1, 4-methylpentenes-1, hexene-1 and octene-1. Out of these, α-olefins having 6 to 8 carton atoms, such as 4-methylpentene-1, hexene-1 and octene-1 can be cited as more preferable examples.

[0031] The melt flow rate (MFR) of the linear low density polyethylene of the present invention is preferably 0.1 to 10 g/10 minutes, more preferably 0.2 to 5 g/10 minutes, much more preferably 0.3 to 3 g/10 minutes, and especially preferably 0.3 to 1.5 g/10 minutes, as' measured at 190° C. and a load of 2.16 Kg in accordance with ASTM D-1238.

[0032] For the linear low density polyethylene of the present invention, either linear low density polyethylene manufactured by use of what is called a single-site catalyst such as a metallocene catalyst or linear low density polyethylene manufactured by use of a Ziegler-Natta catalyst using the magnesium carrier may be used. The linear low density polyethylene of the present invention may be selected from among commercially available polyethylene resins. Particularly, the linear low density polyethylene manufactured by use of a metallocene catalyst is used preferably.

[0033] The density of the high-pressure low density polyethylene of the present invention is preferably 0.910 to 0.930, more preferably 0.910 to 0.925 g/cm³, much more preferably 0.910 to 0.925 g/cm³, and especially preferably 0.915 to 0.925 g/cm³.

[0034] The melt flow rate (MFR) of the high-pressure low density polyethylene of the present invention is preferably 0.1 to 10 g/10 minutes, more preferably 0.1 to g/10 minutes, much more preferably 0.3 to 3 g/10 minutes, as measured at 190° C. and a load of 2.16 Kg.

[0035] The high-pressure low density polyethylene of the present invention may be selected from among commercially available low density polyethylene resins properly.

[0036] 100 weight percent of linear low density polyethylene is preferable as the polyethylene-type resin of the present invention. When the polyethylene-type resin is a composition of linear low density polyethylene and high-pressure low density polyethylene, the ratio of the high-pressure low density polyethylene is preferably less in weight than the linear low density polyethylene. The ratio of high-pressure low density polyethylene in such composition is preferably less than 50 weight percent, more preferably 40 weight percent, and much more preferably 30 to 0.001 weight percent based on 100 weight percent of the composition.

[0037] It can be expected that when a composition the ratio of the high-pressure low density polyethylene of which is 35 to 20 weight percent based on 100 weight percent of the composition is used as the polyethylene-type resin of the present invention, there may be good effects such as the film showing excellent anti-block properties during and after the formation of the film and the web showing high stability during film blowing.

[0038] The polyethylene-type resin of the present invention may be blended with another resin to such extent that the purpose of th present invention will not be defeated. Examples of such another resin include ethylene-α-olefin copolymer, ethylene-vinyl acetate copolymer, ethylene-ethyl acrylate copolymer, ethylene-methyl methacrylate copolymer and olefin-based thermoplastic elastomer. The allowable blending ratio of such another resin is not more than 30 weight percent or so based on the polyethylene-type resin.

[0039] The polyethylene-type resin of the present invention may be blended with additives as required. Examples of such additives include plasticizers, antioxidants, ultraviolet absorbers, heat stabilizers, flame retardants, internal release agents, antistatic agents, surface wetting improving agents, combustion accelerators, pigments and lubricants.

[0040] The tubular article of the present invention is formed by molding the aforesaid polyethylene-type resin into film by the conventionally known method. The water-cooled or air-cooled film blowing method can be used preferably as the method for molding the tubular article.

[0041] The thickness of the film is preferably approximately 60 to 120 μm. In the case in which the film is mold by inflation molding method, the gusseted tubular article for making a bag as specified in the present invention can be obtained by folding the resultant tubular blown film as a gusseted tubular article and cutting it into a desired length. This gusseted tubular article may be used singly as itself.

[0042] The aforesaid gusseted tubular article may be put to use as a bag for packing goods by heat-sealing its one of ends. This bag may be used to transport and store goods after it is filled with the goods from its open end and then the open end is heat-sealed.

[0043] In the case where the gusseted tubular article is sealed by heat sealing, its characteristic is that the sealed four-layer section at the gusset has excellent strength. When the conventionally known gusseted resin bags were transported with goods packed in them they were often broken at the sealed four-layer section due to the low heat-seal strength. However, the effect of the gusseted tubular article of the present invention is noticeable in that breakage hardly occurs in the tubular article due to the sealed section.

[0044]FIG. 1 illustrates a gusseted tubular article of the present invention for making a bag which is made of polyethylene resin to assist in understanding the gusseted tubular article of the present invention. Gusseted Tubular Article 1 in FIG. 1 is illustrated with Gusset 2 in a folded state. And with one end of the gusseted tubular article is heat-sealed at the position of 3. This shows a remarkable effect that breakage hardly occurs at Four-layer Section 6 in which the four layers are folded to overlap. The word of end of the gusseted tubular article includes an end section for heat-sealing and folding to form an end portion of a bag therefrom in the present invention.

[0045] In the gusseted tubular article of the present invention, Sections 4 and 5 may appear in which the tubular article is fused in the areas adjacent to Heat-sealed Section 3. These are apt to take place especially when a gusseted composite tubular article described below is heat-sealed from the outside of the outer layer bag. FIG. 1 shows a condition of the gusseted tubular article in which there is such fused areas.

[0046] A gusseted composite tubular article of the present invention for making a bag which comprises the gusseted tubular article made of the polyethylene-type resin and at least one layer of a gusseted tubular article made of a different material which is put on the outside of the former gusseted tubular article is a preferable, because it exhibits satisfactory heat-sealability, does not require any auxiliary materials such as sewing yarn and crepe paper, and shows excellent workability making automatic packing and sealing possible.

[0047] As examples of the different material of the gusseted tubular article which is put on the outside, materials such as kraft paper, cloth, non-woven fabrics and resin bags can be cited. In particular, kraft paper is especially preferable.

[0048] A gusseted composite tubular article of such structure that both ends of the aforesaid gusseted tubular article made of a different material which is put on the outside are sealable is a preferable embodiment of the present invention.

[0049] Such gusseted composite tubular article can be put to use in transportation and storage after one of its open ends is first sealed and then the other end is sealed after goods are packed in it.

[0050] It is desirable that the inner-layer polyethylene-type-resin tubular article be sealed by means of heat sealing. However, the sealing of the gusseted tubular article made of a different material which is put on the outside may be accomplished by using the conventionally known method.

[0051] Given below is a description of examples of the method for sealing the ends of the gusseted composite tubular article on the basis of a gusseted composite tubular article with the outer layer tubular article made of kraft paper.

[0052] In the first example, one of the front and back walls of the paper tubular article at the end section of the paper tubular article is stairstepped (normally called “stairstepping”) against the other wall. If the outer tubular article is made up of two or more layers, the paper tubular article is stairstepped in such manner that the outermost step protrudes most. When the outside surface of the paper bag and the protruding stairstepped part is bonded by folding the stairstepped part inwards, an adhesive may be applied in advance to the outside surface of the paper bag at the area which will overlap with the stairstepped part, or in advance to the surface of the stairstepped part which will overlap with the paper bag. The inner layer tubular article made of polyethylene-type resin is sealed by heat sealing. The heat sealing of the tubular article made of polyethylene-type resin can be accomplished by pressing a heat sealer from the outer layer tubular article.

[0053] In the second example, a method may be adopted in which one end of the paper tubular article is stairstepped, the stairstepped part is folded together with the polyethylene tubular article previously heat-sealed, and the stairstepped part is bonded and sealed to the outside wall surface in the same manner as described in the first example.

[0054] In the third example, as in the first and second examples, the one end of the outer layer paper tubular articles is cut in a straight line, at least one auxiliary flap is bonded to the outside wall so that a stairstepped part protruding outwards from the end edge, and such auxiliary flap is folded and sealed in the same manner as described in the first and second examples.

[0055] In the fourth example, the one end of the outer layer paper tubular article is cut in a straight line, and the inner layer tubular article made of polyethylene-type resin is sealed by heat sealing. After the end edge is brought into alignment in a straight line, the end can be sealed by using an adhesive with a paper reinforcing paper in such manner that it encloses the end.

[0056] Furthermore, it is also possible to design such structure that the opening tape is attached to the reinforcing paper in the width direction (transverse direction), and the bag may be opened easily by undoing the sealing in the stairstepped part by pulling up the opening tape in the width direction to rip the reinforcing paper.

[0057] In the fifth example, the one end of the outer layer paper tubular article is cut in a straight line, the end edge is brought into alignment in a straight line, the end is folded to enable the end to be bonded and sealed by using an adhesive with a reinforcing paper attached in such manner that it encloses the end. In this case, the strength of the sealing can be improved by carrying out the folding of the ends twice. Even in this case, a piece of opening tape may be attached to the reinforcing paper in the width direction similarly as in the case of the fourth example.

[0058] In the sixth example, either a protruding stairstepped part is formed at the end of the outer paper tubular article or a flap is attached to the end that has been cut in a straight line, and an adhesive layer covered with release paper is provided on the surface thereof so that the end can be sealed by peeling off the release paper at the time of sealing, folding the stairstepped part or the flap, and attaching it to the kraft paper outside wall. (Japanese Laid-open Patent Application 2000-190989.)

[0059] In the seventh example, either a protruding stairstepped part is formed at the end of the outer paper tubular article or a flap is attached to the end that has been cut in a straight line, and an adhesive layer covered with release paper is provided on the outside surface of the stairstepped part so that the end can be sealed by peeling off the release paper at the time of sealing, folding the stairstepped part or the flap, and attaching it to the kraft paper outside wall. (Japanese Laid-open Patent Application 2001-278290.)

[0060] There is no particular limitation on the adhesive used in the present invention. Any known adhesive may be selected properly to be used as the adhesive. When the open end of a gusseted bag has to be sealed in a short time, for example, the use of a hot melt-based adhesive is preferable.

[0061] In packing goods in the gusseted composite tubular article of the present invention and sealing it, it may be sealed at its bottom by any one of aforementioned methods and put to use as a bag for packing goods in it. The method of the aforesaid third example is the most preferable method for sealing the bottom.

[0062] In using the gusseted bag provided as described above, it is a way superior in workability to bond and seal its open end by reactivating the hot melt type adhesive previously applied by means of such heat source as hot air after goods have been packed.

[0063] The bag with a sealed bottom end is packed with goods. Each of the methods of the aforesaid examples may also be used as a preferable method for the purpose of sealing the open end after packing. Out of those methods, the methods of the first to third examples can be cited as preferable methods for sealing the open end.

[0064] Especially, the method in which the bottom end is sealed by the method of the fifth example and the open end is sealed by the method of the second or third example can be cited as a preferable method.

[0065] It is desirable that the sealed end be so structured that a opening tape is attached to a reinforcing paper at the time of sealing the bottom end and the seal can be opened easily by pulling up the opening tape in the width direction to rip the reinforcing paper.

[0066] It is possible to accomplish the heat sealing of the inner layer gusseted tubular article made of polyethylene-type resin in the gusseted composite tubular article of the present invention by applying a heat sealer to the outer tubular article from its outside. As to the heat-sealing conditions for that purpose, relatively low pressure and high temperature are preferable, and a temperature of approximately 290° C. is recommendable. When the gusseted tubular article of the present invention is heat-sealed under such conditions, the areas adjacent to the heat-sealed section may be fused. The condition in which such fusion is found in the adjoining areas is preferable.

[0067] Given below is an explanation of a preferable example of the gusseted composite tubular article, using FIG. 2. Gusseted Composite Tubular Article 18 comprises an outer layer gusseted tubular article made of kraft paper and an inner layer gusseted tubular article made of polyethylene-type resin, with an auxiliary flap attached to the top end of the outer layer kraft paper so that there is a stairstepped part and with the bottom end cut in a straight line.

[0068] A cross-sectional side view of the gusseted composite tubular article is illustrated in FIG. 3 so that its structure may be understood easily. As shown in FIG. 3, Ends 9a and 10a of the two Auxiliary Flaps 9 and 10, the width of which is the same as that of Outside Wall Surface 8a on one side at the end corresponding to the open end of the gusseted composite tubular article, are attached to Outside Wall Surface 8a by means of Adhesive 17. One Auxiliary Flap 9 has a length that the other End 9b can protrude outwards from the open end edge of Gusseted Tubular Article 8, and the other Auxiliary Flap 10 is so positioned that it overlaps the outside of Auxiliary Flap 9 and has a length enabling the other End 10b to protrude outwards beyond End 9b of the inside Auxiliary Flap 9. Hot Melt Adhesive 11 is coated only on the stairstepped parts at the other Ends 9b and 10b of Auxiliary Flaps 9 and 10.

[0069] Given below is an explanation of an example of the sealing of the end of the gusseted composite tubular article of the present invention, using FIG. 4. FIG. 4 illustrates a cross section of the bottom end of the gusseted composite tubular article shown in FIG. 2 which was sealed by carrying out the heat sealing in Location 15 and folding the tubular article twice along Chain Line 16. In FIG. 4, after the inner layer Gusseted Tubular Article 7 was heat-sealed in the area between Two-dot Chain Lines 15, the end section of the tubular article was folded twice along Chain Line 16 and sealed by enclosing and fixing it with Reinforcing Paper 14 with Opening Tape 13.

[0070] Since the heat-sealing strength of the gusseted tubular article of the present invention which is made of polyethylene-type resin is high, any heat-sealing location may be selected arbitrarily, and any sealing method may be selected arbitrarily. For example, the bottom end of the gusseted composite tubular article of FIG. 2 may be sealed in a way as shown in any of FIGS. 5 to 7. In FIG. 5, the folding shown in FIG. 4 is carried out once. In FIG. 6, the location of heat seal of the inner layer tubular article made of polyethylene-type resin shown in

[0071]FIG. 5 has been changed. Furthermore, in FIG. 7, the sealing of the end is carried out without folding the Inner and outer layers.

[0072]FIG. 8 is a cross-sectional drawing showing the sealed condition of the top end of the gusseted composite tubular article of FIG. 2. In FIG. 5, after the end of Inner Layer Tubular Article 7 is heat-sealed in the area between Two-dot Chain Lines 12, the open end of the bag is folded along Chain Une 16, Hot Melt Adhesive 11 is reactivated by heat, the whole of the stairstepped part of the other ends 9b and 10b at Auxiliary Flaps 9 and 10 is bonded to Outside Wall Surface 8b of the gusseted bag, and the end is sealed.

[0073] Since the gusseted composite bag sealed as described above has excellent strength, it has the following characteristics. Namely, there will be no leakage or breakage in transit, a stack of the bags will be kept in good shape, there will be no entry of any foreign material at the time of opening the bags, and the inner layer polyethylene-type resin bag can be removed easily.

[0074] The polyethylene-type resin bag of the present invention also exhibits excellent suitability when it is brought into any place of work requiring rigorous environmental standards, such as clean rooms, after the inner layer bag has been taken out and dust has been removed, and further as required, after treatment such as disinfection has been given.

[0075] The present invention provides a gusseted composite tubular article that makes possible the formation of those bags which are hardly broken and from which the inner layer bag can be removed easily.

[0076] The gusseted composite tubular article for making a bag of the present invention is especially suitable for use in packing heavy goods in it.

EXAMPLES

[0077] The present invention is explain d specifically below by using Examples, but the present invention is not limited to these Examples in any way.

Example 1

[0078] A gusseted composite tubular article for making a bag shown in FIG. 2 comprising a gusseted tubular article of the present invention made of linear low density polyethylene and a gusseted tubular article made of a different material which is put on the outside of the former gusseted tubular article was prepared. That is, Gusseted Composite Tubular Article 18 for making a bag was formed by putting Gusseted Tubular Article 8 made of kraft paper, on the outside of a tubular article which has a size of 38 cm of transverse width, 90 cm of longitudinal length and 21 cm of overall width of gusset, and which comprises a 80 μm thickness film made of a linear low density polyethylene (EVOLUE SP0510 available from Mitsui Chemicals, Inc.) having density of 0.905 g/cm³ and MFR of 1.0 g/10 minutes. Both ends of the gusseted composite tubular article were cut in a straight line.

[0079] Two Auxiliary Flaps 9 and 10 having the same width as that of Gusseted Composite Tubular Article 18 of FIG. 2 are fixed to Gusseted Composite Tubular Article 18 by means of Adhesive 17, and Hot Melt Adhesive 11 is coated on the stairstepped surface at the other Ends 9b and 10b of Auxiliary Flaps 9 and 10.

[0080] As illustrated in FIG. 3, Ends 9a and 10a of two Auxiliary Flaps 9 and 10 having the same width as that of Outside Wall Surface 8a on one side at the open end of the gusseted composite tubular article are fixed to Outside Wall Surface 8a by means of Adhesive 17. One Auxiliary Flap 9 has a length that the other End 9b can protrude outwards from the open end edge of Gusseted Tubular Article 8, and the other Auxiliary Flap 10 is so positioned that it overlaps the outside of Auxiliary Flap 9 and has a length enabling the other End 10b to protrude outwards beyond End 9b of the inside Auxiliary Flap 9. Hot Melt Adhesive 11 is coated only on the stairstepped parts at the other Ends 9b and 10b of Auxiliary Flaps 9 and 10.

[0081] The end corresponding to the bottom in FIG. 2 is heat-sealed in Location 15, folded twice along Chain Line 16 and sealed by endosing and fixing with reinforcing paper 14 with Opening Tape 13 with the result of sealed end as shown in FIG. 4.

[0082] 20 kg of soy bean protein powder were put in this gusseted bag as its contents, and the open end of Inner Layer Tubular Article 7 was heat-sealed in the area between Two-dot Chain Lines 12. After that, the open end of the bag was folded along Chain Une 16 shown in FIG. 3, Hot Melt Adhesive 11 was reactivated by heat, the whole of the stairstepped surface of the other End 9b and 10b at Auxiliary Flaps 9 and 10 was bonded to Outside Wall Surface 8b of the gusseted bag so that the open end was sealed with the result of the sealed end as shown in FIG. 8.

[0083] The strength of the resultant gusseted composite bag with the contents was measured by the method as described below. No bag breakage or power leakage was found.

[0084] Bag-Breakage Resistance Test

[0085] Bag breakage resistance was measured in accordance with JIS Z0217. Three bags were used as the test samples. They were dropped vertically 10 times from a height of 1.2 m. After that, the inner layer bag was removed, and the inner layer bag alone was dropped vertically. The bag after dropped was observed.

Example 2

[0086] A gusseted composite bag was prepared in the same manner as described in Example 1 except that in place of th linear low density polyethylene of Example 1, a mixture of 70 wt % of the same linear low density polyethylene and 30 wt % of a low density polyethylene (F998 available from Mitsui Chemicals, Inc.) having density of 0.922 and a melt flow rate of 0.6 g/10 minutes was used.

[0087] 20 kg of soy bean protein powder were put in this gusseted bag as its contents, and the open end of the bag was sealed by the same method as described in Example 1.

[0088] The strength of the resultant gusseted composite bag with the contents was measured by the same method as described in Example 1. No bag breakage or power leakage was found. 

What we claim:
 1. A gusseted tubular article for making a bag which is made of a polyethylene-type resin comprising 100 to more than 50 weight percent of linear low density polyethylene having density of 0.895 to 0.925 g/cm³ and a melt flow rate of 0.1 to 10 g/10 minute and 0 to less than 50 weight percent of high-pressure low density polyethylene having density of 0.910 to 0.930 g/cm³ and a melt flow rate of 0.1 to 10 g/10 minute.
 2. A gusseted bag obtained by heat-sealing one of the ends of the gusseted tubular article for making a bag described in claim
 1. 3. A gusseted composite tubular article for making a bag which comprises the gusseted tubular article described in claim 1 and a gusseted tubular article made of a different material which is put on the outside of the former gusseted tubular article.
 4. A gusseted composite tubular article for making a bag according to claim 3 wherein the different material is kraft paper.
 5. A gusseted composite tubular article for making a bag according to claim 3 or 4 wherein the gusseted tubular article made of a different material which is put on the outside is so structured that both of its ends are sealable.
 6. A composite gusseted bag obtained from the gusseted composite tubular article described in any one of claims 3 through 5, which is so structured that one of its ends is in alignment in a straight line at its end edge, and the end is sealed and folded, and the end is enclosed and fixed by a reinforcing paper with an opening tape to form a bottom section.
 7. A composite gusseted bag according to claim 6 wherein a opening end of the tubular article has either a stairstepped section formed by extruding layers like stairs or at least one auxiliary flap so bonded to the outside wall surface that it forms a stairstepped surface protruding outside which can seal th opening end with a hot melt adhesive coated on its surface.
 8. A composite gusseted bag according to claim 7 wherein the opening tape is attached in the width direction to the section which can form the seal. 